The ability to accurately position a driver outside of a vehicle in relation to the vehicle can support several uses. For example, when locking and unlocking the car it may be required that the driver must be within a certain range of the vehicle, thereby making it important with an accurate determination of the position of the driver.
Other actions which may require accurate positioning of a driver or a user device held by the driver may be starting the vehicle and opening the trunk lid. It may also be possible to move the car from a position outside of the vehicle by using movement of the user device to control movement of the vehicle.
One well known positioning method for electronic devices is to use a GPS device. However, for many applications, the accuracy of a GPS device may not be sufficient. Moreover, there are circumstances where a GPS device cannot be used due to a lack of reception, such as in a parking garage and in dense city environments.
Presently known general positioning solutions with higher accuracy typically build on either the Time-of-Arrival (TOA) principle, or the Time-Difference-of-Arrival (TDOA) principle. For a TOA-method, three receiver stations are required for obtaining a 3D position (x,y,z), and with two receiver stations it is only possible to obtain a 2D position (x,y). For a TDOA-method four receivers are required for determining a position in three dimensions.
Since each additional sensor required in the vehicle adds to the cost of the vehicle, it is desirable with improved solutions for determining a position of a user device in relation to a vehicle with reduced system requirements.